A good positional decision. It's true that White exchanges Black's backward pawn on d6, but he is the one benefiting from the opening of the d-file.
27... g8h7  28. e3f2 A difficult move. Aronian is in no hurry, and although I don't understand exactly what the benefits of this move are (maybe preventing h5-h4 $2), Black doesn't have much to do anyway. 28... c6c8  29. d5b6  29... c8d8 